HIGH EFFICIENCY SUPERCHARGER OUTLET
TECHNICAL FIELD
The present invention relates to a positive displacement air pump employed as a
supercharger for an internal combustion engine, including a positive displacement air pump
employed as a supercharger and having a modified outlet port to improve isentropic efficiency.
BACKGROUND
Positive displacement air.pumps include Roots-type blowers, screw-type air pumps,
and many other similar devices with parallel lobed rotors. Positive displacement air pumps may
include lobed rotors having either straight lobes or lobes with a helical twist. The rotors may be
meshingly disposed in parallel, transversely overlapping cylindrical chambers defined by a
housing. Each rotor may have four lobes in conventional embodiments, although each rotor may
have fewer or more lobes in other embodiments. Spaces between adjacent unmeshed lobes of
each rotor may transfer volumes of compressible fluid (e.g., air) from an inlet port to an outlet
port opening, with or without mechanical compression of the fluid in each space prior to
exposure of the transfer volumes to the outlet port opening. The ends of the unmeshed lobes of
each rotor may be closely spaced from the inner surfaces of the cylindrical chambers to effect a
sealing cooperation therebetween. As the rotor lobes move out of mesh, air may flow into
volumes or spaces defined by adjacent lobes on each rotor. The air in these volumes may be
trapped therein at substantially inlet pressure when the meshing lobes of each transfer volume
move into a sealing relationship with the inner surfaces of the cylindrical chambers. Timing
gears may be used to maintain the meshing lobes in closely spaced, non-contacting relation to
form a seal between the inlet port and outlet port opening. The volumes of air may transferred or
directly exposed to the outlet port when the lobes move out of sealing relationship with the inner
surfaces of the cylindrical chambers.

Conventionally, positive displacement air pumps may be used as superchargers for
vehicle engines, wherein the engine provides the mechanical torque input to drive the lobed
rotors. The volumes of air transferred to the outlet port may be utilized to provide a pressure
"boost" within the intake manifold of the vehicle engine, in a manner that is well known to those
of ordinary skill in the art. The power or energy required to transfer a particular volume of air
under certain operating conditions may be used in evaluating the efficiency of a positive
displacement air pump. To pump the fluid (e.g., air) using a supercharger requires that
mechanical energy be placed into the supercharger. The required mechanical energy input is
directly related to the various efficiencies (e.g., mechanical, isentropic, etc.) and operating
conditions of the supercharger(e.g., mass flow rate, pressure ratio, etc.). For the same operating
conditions, if the efficiency is improved, the required mechanical energy input is decreased, thus
benefiting efficiency of the overall system that the supercharger is applied to (e.g., an internal
combustion engine). An ideal process would be 100% efficient. However, actual compression
will operate at an efficiency below this level. The actual compression relative to the ideal
process is called isentropic efficiency. The temperature of the air being transferred may increase
as the air flows through the supercharger. By improving isentropic efficiency, less excessive
heat energy may be put into the fluid (e.g., air) to achieve the desired pressure for the fluid (e.g.,
air).
Previous attempts have been made to improve the isentropic efficiency of positive
displacement air pumps, such as Roots-type blowers, by improving the configuration of the
outlet port. For example, the outlet port of a Roots-type blower may be configured as disclosed
and illustrated in U.S. Patent No. 5,527,168, which is hereby incorporated by reference in its
entirety. As technological improvements have been made to supercharger rotor geometry
(including, for example, the degree of helical twist), the fluid velocity has been shifted more
towards the axial direction, as opposed to the radial direction. However, current parallel shaft
supercharger outlet port geometry may continue to account mainly for radial outlet airflow,
rather than significantly addressing the axial flow component of the fluid velocity.

It may be desirable to optimize flow geometry at the outlet end of the supercharger
to better account for both the axial and radial fluid velocity, while still maintaining the
conventional and/or standard features of a supercharger, such as an axial inlet direction and a
radial outlet port direction. As supercharger speed increases, the axial velocity component may
also increase and may require a more drastic velocity change as it exits the outlet port of a
conventional supercharger design. In particular, all axial velocity vectors may be required to be
converted into radial velocity vectors, thereby increasing the work that must be performed on the
fluid.
SUMMARY
A supercharger is provided that may include a housing having a first end and a
second end. The housing may at least partially define a chamber and may include at least one
rotor disposed within the chamber. The supercharger may further include an inlet port proximate
the first end of the housing and in fluid communication with the chamber and an outlet port
proximate the second end of the housing and in fluid communication with the chamber. The
supercharger may further include a relief chamber in fluid communication with the chamber. In
an embodiment, the relief chamber may extend in the axial direction and may have a depth in the
axial direction that is equal to at least about 10% of the axial length of the rotor.
An improved outlet port geometry for a supercharger in accordance with an
embodiment of the present invention may allow for retaining the standard or conventional
features of a supercharger, including an axial inlet and a radial outlet, while decreasing the
excess work performed on the fluid. An improved outlet port geometry may be used to generate
an optimal flow path for the fluid as it exits the supercharger. An improved outlet port geometry
for a supercharger be especially useful for improving performance in the high flow and/or high
speed portion of the supercharger operating range. By increasing performance in the high flow
and/or high speed portion of the operating range, a smaller supercharger may be used to achieve

increased performance. The utilization of a smaller supercharger may significantly decrease
packaging size requirements and costs.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings, wherein:
FIG. 1 is view of a supercharger according to an embodiment of the present
invention.
FIG." 2 is a cross-sectional view of a portion of a supercharger according to an
embodiment of the present invention;
FIG. 3 is a view of a supercharger according to an embodiment of the present
invention;
FIG. 4 is a cross-sectional view of a portion of a supercharger according to an
embodiment of the present invention;
FIG. 5 is a cross-sectional view of a portion of a supercharger according to an
embodiment of the present invention.
FIG. 6 is a perspective view of a bearing plate according to an embodiment of the
present invention;
FIG. 7A is a top plan view of a prior art bearing plate including a prior art relief
chamber;
FIG. 7B is a top plan view of a bearing plate including a relief chamber according
to an embodiment of the present invention;
.4.

FIG. 8 is a perspective view of a prior art bearing plate including a prior art relief
chamber;
FIG. 9A is a front view of a prior art bearing plate including a prior art relief
chamber;
FIG. 9B is a front view of a bearing plate including a relief chamber according to
an embodiment of the present invention;
FIG. 10 is a chart of isentropic efficiency versus supercharger speed, comparing the
prior 'art device with the present invention.
DETAILED DESCRIPTION
Reference will now be made in detail to embodiments of the present invention,
examples of which are described herein and illustrated in the accompanying drawings. While the
invention will be described in conjunction with embodiments, it will be understood that they are
not intended to limit the invention to these embodiments. On the contrary, the invention is
intended to cover alternatives, modifications and equivalents, which may be included within the
spirit and scope of the invention as embodied by the appended claims.
Referring now to FIGS. 1-2, the supercharger (e.g., positive displacement air
pump) 10 may include a main housing 12 and a bearing plate 14. The supercharger 10 may
include a longitudinal axis 13. The main housing 12 and bearing plate 14 may be secured
together in any manner known to those of ordinary skill in the art. For example, the housing 12
and bearing plate 14 may be secured together by a plurality of machine screws (not shown) with
the appropriate alignment being insured by means of a pair of dowel pins (not shown). Although
the main housing 12 and bearing plate 14 have been described as comprising separate members,
this may not be the case in other embodiments and they may be integral and/or unitary members
in other embodiments. For example and without limitation, the housing and bearing plate may
form an integral and/or unitary and/or monolithic structure. When the housing and bearing plate

are integrated, the outlet geometry for the supercharger would be the same as described herein,
but the supercharger would comprise one component, rather than two components. For example
and without limitation, referring now to FIGS. 3-4, the supercharger 100 is shown as having an
integrated housing and bearing plate design 112.
While the positive displacement air pump or supercharger 10,100 may comprise a
Roots-type blower or a screw-type air pump in some embodiments, the positive displacement air
pump 10, 100 may comprise any type of positive displacement air pump with rotors (e.g., lobed
rotors) in other embodiments. For example, the positive displacement air pump 10,100 may
comprise any air pump with parallel lobed rotors.
The main housing 12, 112 may be a unitary member defining inner cylindrical wall
surfaces and a transverse end wall 18. The bearing plate 14 may define a bearing plate end wall
20 in some embodiments. In other embodiments, a separate bearing plate may not be utilized.
Instead, a single component serving the function of the housing and bearing plate may be
utilized, and the single component may define an end wall 120 opposite the transverse end wall
18. The inner cylindrical wall surfaces of main housing 12 and the end walls 18,20 or 120 (of
the housing 12 or the housing and bearing plate structure 112, for example) may together define
a plurality of transversely overlapping cylindrical chambers 22. In an embodiment, there may be
two overlapping cylindrical chambers 22.
A plurality of rotors 23 may be disposed within the overlapping cylindrical
chambers 22. Each of the rotors 23 may have four lobes. Although four lobes are mentioned in
detail, each of the rotors 23 may have fewer or more lobes in other embodiments. Each of the
rotors 23 may be mounted on a rotor shaft for rotation therewith. Each end of each rotor shaft
may be rotatingly supported within the bearing plate 14 or a single component housing by means
of a bearing set (not shown). At least one of the rotors 23 may utilize any of various input drive
configurations(an input shaft portion and/or step up gear set, for example and without limitation)
by means of which the supercharger 10 may receive input drive torque.

Main housing 12,112 may include a first end a second end. The first end of main
housing 12,112 may include a backplate portion 24. Backplate portion 24 may be formed
integrally with main housing 12 in some embodiments, or may comprise a separate plate member
in other embodiments. Backplate portion 24, whether integral with or separate from the housing
12,112, may define ah inlet port 26. The inlet port 26 may be in fluid communication with at
least one of the chambers 22 in which the rotors.23 are disposed. Main housing 12, 112 may
also define an outlet port 28. The outlet port 28 may be proximate the second end of main
housing 12,112. The outlet port 28 may also be in fluid communication with at least one of the
chambers 22 in which the rotors 23 are disposed. The outlet port 28 may include a port end
surface 30 and a pair of oppositely disposed port side surfaces (not shown). The port end surface
30 may be substantially perpendicular to the longitudinal axis 13 of supercharger 10 in an
embodiment as shown in FIG. 2. However, the port end surface 30 may be angled in other
embodiments (e.g., not substantially perpendicular to the longitudinal axis 13 of supercharger
10). For example, as shown in FIG. 5, the port end surface may be angled outwardly by an angle
a. Angle a may be less than 45° in an embodiment. Although angle a specifically mentioned as
being less than 45° angle a may be larger or smaller in other embodiments.
The main housing 12 may include an end portion 29 in some embodiments, which
may function as a receiving portion for the bearing plate 14. The end portion 29 may be
proximate the second end of main housing 12. In other embodiments, a separate bearing plate
may not be utilized and housing 112 may include an integral bearing plate structure at the second
end of the housing 112. In these other embodiments where the bearing plate structure is integral
with the housing 112, a receiving portion for a bearing plate in the housing 112 may not be
necessary.
Referring now to FIG. 6, a bearing plate 14 may be provided to enable assembly of
the supercharger 10. However, as described herein, a bearing plate 14 may be omitted in other
embodiments of the invention (e.g., FIGS. 3-4). For example, in other embodiments of the
invention, the structure of the bearing plate may be integrated with the housing 112. In

accordance with an embodiment of the invention in which a separate bearing plate 14 may be
utilized, the bearing plate 14 may comprise a first portion 31 and a second portion 33. The first
portion 31 may be connected to and/or integral with the second portion 33. The first portion 31
may be of an approximately rectangular-type shape and may have a certain thickness that is
constant. The first portion 31 of the bearing plate 14 may include a plurality of apertures for
receiving a plurality of fasteners to connect the bearing plate 14 to the main housing 12. The
second portion 33 of the bearing plate may be of an approximately dumbbell-type shape and may
have a certain thickness that is generally greater than that of the first portion 31.
The second portion 33 of the bearing plate 14 may include and/or define a relief
chamber 32. The relief chamber 32 may be provided to assist in reducing drive horse power and
increasing iseritropic efficiency. In particular, a portion of the fluid that is being transferred from
the inlet port 26 to the outlet port opening 28 may exit axially from the end of the rotors (as
opposed to that portion of the fluid which may exit radially). The region of the supercharger 10
in which the fluid may exit axially from the end of the rotors may be coextensive with the relief
chamber 32. The relief chamber 32 may include and/or be defined in part by a chamber end
surface 34. The relief chamber 32 may face inwardly toward the overlapping cylindrical
chamber 22 in which the rotor 23 is disposed. The relief chamber 32 may be in fluid
communication with the cylindrical chamber 22 in which the rotor 23 is disposed. The relief
chamber 32 may extend in the axial direction and may extend beyond cylindrical chamber 22 in
the axial direction toward the second end of the housing 12.
Although the relief chamber 32 is described and shown in detail as being formed
and/or placed in a bearing plate 14, the relief chamber 32 may also be formed in other structures
in other embodiments of the invention. For example, the relief chamber 32 may be formed in an
integral portion of the housing 112 in another embodiment. The relief chamber 32 may also be
formed in any other suitable structure at the second end of the housing that opposes the first end
including inlet 26 in other embodiments. This structure may be integral with and/or separate
from the housing 12. In these embodiments that do not include separate bearing plate 14, the

function of the relief chamber 32 may be substantially the same as when the relief chamber is
included in the bearing plate 14 and the geometries of the outlet port 28 may be substantially the
same as when the relief chamber is included in the bearing plate 14.
The chamber end surface 34 may be substantially curved (e.g., sloping upward)
from a front edge 36 to a back edge 38. In other embodiments, the chamber end surface 34 may
have substantially less of a curved geometry (see, e.g., FIG 4), but the relief chamber 32 may still
be configured to function substantially the same. In some embodiments/the chamber end
surface 34 may be in a plane generally perpendicular to the bearing plate 14 near the front edge
36. The chamber end surface 34 may be in a plane generally parallel to the bearing plate 14 near
the back edge 38. The front edge 36 may include a plurality of curves and indentations. For
example, the front edge 36 may include at least three curves with two indentations disposed
therebetween in an embodiment. Although three curves and two indentations are mentioned in
detail, the front edge 36 may include fewer or more curves and/or indentations in other
embodiments. The curves and indentions in the front edge 36 may also define the chamber end
surface 34, such that at least a portion of the chamber end surface 34 may have a substantially
corresponding number of bumps and valleys. The front edge 36 may be straight in other
embodiments of the invention. In at least some embodiments, the front edge 36 may be
configured to substantially correspond in size and/or shape to the size and/or shape of the lobed
rotors disposed within the overlapping, cylindrical chambers 22 of the housing 12. The back
edge 38 of the relief chamber 32 may include a plurality of curves and an indentation. For
example, the back edge 38 may include at least two curves in an embodiment with an indentation
disposed therebetween. Although two curves and a single indentation are mentioned in detail,
the back edge 38 may include fewer or more curves and/or indentations in other embodiments.
Although the back edge 38 may include one or more curves and/or indentations, the chamber end
surface 34 near the back edge 38 may be flat. The back edge 38 may be straight in other
embodiments of the invention.

The relief chamber 32 may also be defined by a pair of oppositely disposed
chamber side surfaces 40,42. Each of the chamber side surfaces 40, 42 may be angled
outwardly from the relief chamber 32 in an embodiment. For example, as best shown in FIG.
7B, the chamber side surfaces 40,42 may be angled at p degrees. The angle (3 may be
approximately 22° in accordance with an embodiment. The angle β may range from about 10° to
about 40° in some embodiments. Although these angles are mentioned in detail, the angle p may
be greater or smaller in other embodiments. In other embodiments, each of the chamber side
surfaces 40,42 may not be substantially linear as illustrated. For example and without
limitation, the chamber side surfaces 40,42 may be substantially curved. The chamber side
surfaces 40, 42 may be configured to substantially correspond in geometry to the geometry of the
lobes of the rotors disposed within supercharger 10,110.
Referring now to FIG. 8, a prior art bearing plate 14' including and/or defining a
relief chamber 32' is shown. The relief chamber 32' may be defined by a chamber end surface
34' and a pair of oppositely disposed chamber side surfaces 40', 42'. Referring now to FIG. 9A-
9B, a difference between the prior art relief chamber 32' and the relief chamber 32 of the present
invention may be illustrated. In'particular, the depth D of the relief chamber 32 in the axial flow
direction may be increased in accordance with the present invention. The depth D of the relief
chamber 32 in the axial flow direction may substantially correspond and/or relate to supercharger
displacement, rotor size, and/or rotor length. In accordance with an embodiment of the
invention, the depth D of the relief chamber 32 may be approximately equal to at least 10% of
the supercharger rotor length. In some embodiments, the depth D of the relief chamber 32 may
approximately equal to about 10% to about 35% of the supercharger rotor length. For example
and without limitation, the relief chamber 32 of the bearing plate 14 may have a depth D of about
20 mm. In accordance with some embodiments of the invention, the relief chamber 32 may have
a depth D that is about twice as deep than the depth D' of the prior art relief chamber 32'. The
depth D may be greater or smaller in other embodiments, in particular depending upon the rotor
size, rotor length, and/or supercharger displacement. Although certain percentages of the

supercharger rotor length are mentioned in detail, the depth D of the relief chamber 32 may be a
smaller or larger percentage of supercharger rotor length in other embodiments. Although
certain depths may be mentioned in detail, the depth D of the relief chamber 32 may be greater
or smaller in other embodiments.
•Referring again to FIG. 7A-7B, another difference between the prior art relief
chamber 32' and the relief chamber 32 of the present invention may be illustrated. In particular,
the width of the relief chamber may be increased in bearing plate 14 of the present invention.
For example and without limitation, the relief chamber 32 may have a width W that is equal to at
least about 50% of the width of the chamber 22 in which the rotor 23 is disposed. For another
example, the relief chamber 32 may have a width W that is about 50% wider than the width W
of relief chamber 32'. The width W may be greater or smaller in other embodiments. The width
W of the relief chamber 32 may be configured to substantially correspond in geometry to the
geometry of the lobes of the rotors disposed within supercharger 10.
Still referring to FIGS. 7A-7B, another difference between the prior art bearing
plate 14' and the bearing plate 14 of the present invention is illustrated. For example and without
limitation, the bearing plate 14 may be smaller in height H than the height H' of the prior art
bearing plate 14'. Furthermore, the number of fasteners necessary to secure the bearing plate 14
to main housing 12 in an embodiment of the invention may be reduced. For example and
without limitation, approximately six fasteners may be used to secure bearing plate 14 to main
housing 12, whereas conventional bearing plates 14' may use at least eight fasteners. Although
these numbers of fasteners are mentioned in detail, fewer or more fasteners may be used in other
embodiments. Reductions in the size of the bearing plate 14 for the supercharger 10 result in
decreases in package size and cost, while maintaining the same amount of fluid flow.
Referring now primarily to FIG. 10, a chart of isentropic efficiency versus
supercharger speed, comparing the prior art device (e.g., having a relief chamber 32' as shown in
FIG. 8) with the present invention (e.g., having a relief chamber 32 as shown in FIG. 6), is

illustrated. The testing which led to the chart of FIG. 10 was performed on a pair of Roots-type
blower superchargers operated at the same pressure and may provide information regarding the
isentropic efficiency (as a percent) versus supercharger speed (e.g., the speed of the input drive
mechanism and/or-configuration). The isentropic efficiency of a device is the actual
performance of the device (e.g., work output) as a percent of that which would be achieved under
theoretically ideal circumstances (i.e., if no heat loss occurred in the system).- In other words, in
the case of a supercharger, the isentropic efficiency is an indication of the amount of input
energy being wasted as heat.
As may be seen in FIG. 10, the invention and the prior art are both about 74%
efficient at a medium supercharger speed of about 10000 RPM. However, when the
supercharger speed is increased to about 18000 RPM, the prior art device with the conventional
outlet utilizing relief chamber 32' has dropped to about 61% efficiency, while the device of the
present invention with the improved relief chamber 32 is still around 73% efficient.
Accordingly, the prior art device is only about 89% as efficient at high supercharger speeds as
the prior art device is at medium supercharger speeds. On the other hand, the device of the
present invention is still about 98% as efficient at high supercharger speeds as the device of the
present invention is at medium supercharger speeds. In an embodiment, the isentropic efficiency
of the supercharger at about 18000 RPM may be at least about 95% of the isentropic efficiency
of the supercharger at about 10000 RPM. The device of the present invention is substantially
more efficient than the prior art device at high blower speeds (e.g., about 18000 RPM), which is
the situation where isentropic efficiency is of greatest concern. The device of the present
invention utilizing improved relief chamber 32 also maintains about the same isentropic
efficiency at medium blower speeds (e.g., about 10000 RPM) as the prior art device utilizing
relief chamber 32' does at the same blower speeds. The improved outlet utilizing relief chamber
32 also does not decrease flow.
Although the efficiency of the present invention may be at least about 70% efficient
at about 18000 RPM at certain pressure ratios (e.g., a pressure ratio of 1.6 as illustrated in FIG.

10), the efficiency of the present invention may increase or decrease depending upon the
pressure ratio and/or mass flow (kg/hr) for the supercharger. Accordingly, the efficiency may be
higher or lower than 70% at high supercharger speeds under other conditions. However, the
isentropic efficiency (%) of a supercharger with an improved outlet utilizing relief chamber 32
may generally be greater than the isentropic efficiency (%) of a supercharger with an outlet
utilizing prior art relief chamber 32' at higher supercharger speeds, even at different pressure
ratios and mass flow rates.
The foregoing descriptions of specific embodiments of the present invention have
been presented for purposes of illustration and description. They are not intended to be
exhaustive or to limit the invention to the precise forms disclosed, and various modifications and
variations are possible in light of the above teaching. The embodiments were chosen and
described in order to explain the principles of the invention and its practical application, to
thereby enable others skilled in the art to utilize the invention and various embodiments with
various modifications as are suited to the particular use contemplated. The invention has been
described in great detail in the foregoing specification, and it is believed that various alterations
and modifications of the invention will become apparent to those skilled in the art from a reading
and understanding of the specification. It is intended that all such alterations and modifications
are included in the invention, insofar as they come within the scope of the appended claims. It is
intended that the scope of the invention be defined by the claims appended hereto and their
equivalents.

We Claim:
1. A supercharger comprising:
a housing at least partially defining a chamber, the housing having a first end and a
second end;
at least one rotor disposed within the chamber;
an inlet port proximate the first end of the housing and in fluid communication with the
chamber;
an outlet port proximate the second end of the housing and in fluid communication with
the chamber; and
a relief chamber in fluid communication with the chamber, wherein the relief chamber
extends in the axial direction and has a depth in the axial direction that is equal to at least about
10% of the axial length of the rotor.
2. A supercharger according to claim 1, further comprising a bearing plate connected to the
housing at the second end of the housing, wherein the relief chamber is included in the bearing
plate.
3. A supercharger according to claim 1, wherein the relief chamber is included in the
housing.
4. A supercharger according to claim 1, wherein the housing includes a plurality of
chambers.
5. A supercharger according to claim 4, wherein each of the plurality of chambers is
overlapping.
6. A supercharger according to claim 1, wherein the rotor is lobed and comprises at least
four lobes.

7. A supercharger according to claim 1, further comprising an input shaft configured to
provide torque to the rotor.
8. A supercharger according to claim 1, wherein the outlet port includes a port end surface
and a pair of oppositely disposed port side surfaces.
9. A supercharger according to claim 8, wherein the supercharger includes a longitudinal
axis and the port end surface is substantially perpendicular to the longitudinal axis.
10. A supercharger according to claim 8, wherein the supercharger includes a longitudinal
axis and the port end surface is not substantially perpendicular to the longitudinal axis.
11. A supercharger according to claim 1, wherein the relief chamber is configured to receive
fluid that exits axially from the chamber in which the rotor is disposed.
12. A supercharger according to claim 1, wherein the relief chamber includes a chamber end
surface that is substantially curved from a front edge to a back edge.
13. A supercharger according to claim 12, wherein the front edge is configured to
substantially correspond to the shape of the rotor.
14. A supercharger according to claim 1, wherein the relief chamber includes a pair of
oppositely disposed chamber side surfaces.
15. A supercharger according to claim 14, wherein each of the chamber side surfaces
includes a portion angled outwardly from the relief chamber.
16. A supercharger according to claim 14, wherein each of the chamber side surfaces
includes a curved portion.
17. A supercharger according to claim 1, wherein the relief chamber has a depth in the axial
direction that is equal to about 10% to about 35% of the axial length of the rotor.
18. A supercharger according to claim 1, wherein the relief chamber has a width that is equal
to at least about 50% of the width of the chamber in which the rotor is disposed.

19. A supercharger according to claim 1, wherein the isentropic efficiency of the
supercharger is at least about 70% at supercharger speeds of at least about 18000 RPM.
20. A supercharger according to claim 1, wherein the isentropic efficiency of the
supercharger at about 18000 RPM is at least about 95% of the isentropic efficiency of the
supercharger at about 10000 RPM.

A supercharger is provided that includes a housing
having a first end and a second end. The housing may at
least partially define a chamber and may include at
least one rotor disposed within the chamber. The
supercharger includes an inlet port proximate the first
end of the housing and an outlet port proximate the
second end of the housing. The supercharger further
includes a relief chamber in fluid communication with
the chamber. In an embodiment, the relief chamber may
extend in the axial direction and may have a depth in
the axial direction that is equal to at least about 10%
of the axial length of the rotor.